2.8 Principled glass shader doesn't show any thickness?
Right figured this out, sorry my fault it wasn't actually a transmission issue (that was set to 1, I must of been fiddling with it when I took the screen shot). So the issue did occur even with a transmission of 1.

The problem was I think with everything being a bit flat. So I added a few edge loops and added a bit of curve to the base, making it more parabolic(?). Also, made sure I didn't have any extra faces hidden in the base.

Also used all the setting recommended above (thanks everyone, much appreciated) ie.


blend type to "Alpha Blend" in settings for the material
See if mesh object doesn't have negative scale and has its normals calculated inside
“screen space refractions” turned in settings for the material